Children under 2 years of age are most susceptible to acute respiratory infections caused by Bordetella pertussis, Haemophilus influenzae type b, Streptococcus pneumoniae and Neisseria meningitidis. We analysed milk samples and sera from mother-infant pairs for specific antibodies that may enhance protection against the bacterial pathogens. The results show that the breast-milk samples contained significant titres of specific IgG and IgA antibodies to the four organisms, although the mean IgG antibody levels were higher in maternal sera than in breast-milk. On the other hand, the mean IgA antibody levels to the four organisms were higher in breast-milk than in both maternal and infant sera. IgM antibodies to these organisms were relatively low or absent in many milk and serum samples. Nevertheless, the significant concentrations of specific IgG and IgA antibodies in milk samples may indicate a protective role for breast-milk against the four infections in early childhood.